Conventionally, an articulated robot arm mechanism has been used in various fields such as an industrial robot. The inventors have developed a linear extension and retraction mechanism that can be applied to an articulated robot arm mechanism like this (Patent Literature 1). The linear extension and retraction mechanism has a first and a second piece strings. The first piece string is formed by connecting a plurality of metallic pieces (first pieces) that have a flat plate shape and are bendably connected to one another with a hinge structure, in a string shape. The second piece string is formed by connecting a plurality of metallic pieces (second pieces) that have a groove frame shape and are bendably connected to one another with a bearing structure in bottom plates, in a string shape. Leading pieces of the first and the second piece strings are connected at tips, and when the first and the second piece strings are fed out forward, the first and the second piece strings are overlapped with each other with a roller unit, have a rigid state secured, and are configured to be a columnar arm having fixed rigidity. When the first and the second piece strings are pulled backward, the first and the second piece strings are separated behind the roller unit, return to a bendable state respectively, and are stored in a storage section inside a support column. Adoption of the linear extension and retraction mechanism to an articulated robot arm mechanism makes an elbow joint section unnecessary, and can easily eliminate a singular point, which makes it a very useful mechanism. Therefore, the linear extension and retraction mechanism can be combined with various joints such as a rising and lowering rotation joint and a turning rotation joint. For example, when a rising and lowering rotation joint is installed directly before the linear extension and retraction mechanism, a positional relationship between the roller unit of the linear extension and retraction mechanism, and the storage section storing the first and the second piece strings changes in accordance with rising and lowering movement of the rising and lowering rotation joint which is interposed between the roller unit and the storage section, and a space between the roller unit and the storage section also changes in width.
The first and the second piece strings repeat reciprocating movement between the storage section and the roller unit. If the space between the roller unit and the storage section is large, there is a possibility that the first and the second pieces deviate from a planned trajectory, and collide with surrounding components, in the process of the reciprocating movement of the first and the second piece strings. Collision of the first and the second pieces with the components not only breaks the components but also could damage the first and the second pieces. Further, as a result that the first and the second piece strings deviate from the planned trajectory, smooth feeding/and pulling-back operation of the arm is likely to be inhibited. In order to reduce these risks, it is necessary to install a mechanism that guides the first and the second pieces, in the space between the storage section and the roller unit.